This application claims benefit of U.S. Provisional Application No. 60/006020 filed Oct. 23, 1995.
1. Field of the Invention
The invention relates to a low power, point to multi-point, multi-function cellular television systems; and more particularly, to such systems transmitting at super high frequencies.
2. Description of the Prior Art
The localized microwave distribution system described in U.S. Pat. No. 4,747,160 includes a plurality of transmitter stations operating at low power in a corresponding plurality of cells. Each transmitter station has a substantially omni-directional transmitting antenna. Each subscriber receiving station has a respective directional receiving antenna, directed so as to receive television signals from only one of the transmitting antennas.
In this prior art system, all of each cell receives signals from the cell transmitter at the same frequency or plurality of frequencies, and the same polarization. When the cells are arranged with the centers of each cell in a rectangular grid pattern, the antenna of a subscriber located close to one of the grid lines faces both its own cell transmitter and also the transmitter of the adjoining cell in the direction the subscriber's antenna is facing. Therefore this subscriber's antenna can receive a weak interfering signal from the more distant transmitter. However, according to the '160 patent, the signal from the-adjoining cell's transmitter is polarized oppositely to the transmitter of the subscriber's own cell, such as vertically instead of horizontally. This provides a great improvement in the discrimination against the signal from the remote transmitter, so that ghost signals are not a problem. However, whenever terrain or other considerations prevent use of an approximately rectangular grid pattern, the advantages of this arrangement are reduced.
Another approach to distribution of telecommunications signals is exemplified by the Xerox Telecommunications network (XTEN), described in a document filed with the FCC. FIG. 7 of that proposal shows that signals are radiated in each cell over four sector antennae, each covering one quarter of the cell, and each sector radiating at all different frequency. The transmitting arrangements are disposed in straight columns, with adjacent columns aligned such that a transmitting arrangement in one column is equally spaced from two adjoining transmitting arrangements of the next column. All transmitting arrangements in a column radiate one polarization in the two quadrants to one side, and the other polarization to the other side. A pattern of polarization selection is so arranged that a subscriber is protected from interference by an adjoining transmitting arrangement in the next column by frequency diversity; and from interference by transmitters in the second column to one side by polarization diversity. This system suffers the disadvantage that each subscriber has access to only one quarter of the frequency spectrum used by the system.